JP2008225169A - Method for forming geometrical pattern - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for forming a geometrical pattern with which a desired geometric pattern is formed on a surface of a work piece. <P>SOLUTION: The work piece is irradiated with a laser beam, and a plurality of hollows holding gaps in between are formed on the surface of the work piece in an array with a two-dimensional periodicity. Next, the work piece is etched, and the etching is continued until the recessions having spread from the respective hollows as centers interfere with one another so as to make boundaries of the recessions form a desired geometric pattern. The method for forming the geometrical pattern does not require large-scaled apparatus or troublesome and complex processes, and can accurately form the desired geometrical pattern on the surface of the work piece. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method of forming a geometric pattern such as a regular triangle, a square, a rectangle, a regular hexagon, etc. on the surface of a workpiece such as glass, and the like, and a fine geometric pattern is formed by combining laser processing and chemical processing. Is to do.

In recent years, with the increase in functionality of industrial products, the relationship between the surface state of objects and surface functions such as optical properties and tribological properties (friction performance and lubrication performance) has attracted attention. The development of new functional products using high-value-added products and the surface function of fine irregularities has been actively conducted.
For analysis of these surface functions, it is necessary to form fine irregularities of a desired shape on the object surface and measure various characteristics.
Conventionally, most of fine pattern processing on an object surface is performed by molding by a machining process or a semiconductor process. However, these processing methods require time and labor to produce a mold and a mask, and the process is complicated.
On the other hand, laser processing enables flexible precision microfabrication without using a mold or a mask.

The present inventors have previously developed a method of forming concave lens-shaped dimples having a smooth surface on a glass substrate by combining laser processing and etching processing (Patent Document 1 below).
In this method, the surface of the glass substrate is irradiated with a laser to form a recess, and then this glass substrate is subjected to isotropic etching. FIG. 8 is a schematic cross-sectional view of the surface 100 of the glass substrate before etching in which the depression 110 is formed by laser irradiation and the surface 120 of the glass substrate in a state where etching has progressed. By etching, the peripheral surface of the depression 110 and the flat surface without the depression are equally removed by etching, so that the diameter of the depression expands without changing the depth d of the depression, and the depression (dimple) 130 is precisely It is molded into a concave lens shape approximating a spherical surface.

FIG. 9A shows a cross-sectional SEM (scanning electron microscope) image of a depression formed by irradiating soda-lime glass with a laser with a peak output of 28 kw and an irradiation time of 0.1 second, and FIG. This shows an SEM image of dimples obtained by etching this in a hydrofluoric acid aqueous solution at about 40 degrees for 4 hours.
In this way, by combining laser processing and etching processing, a concave lens-shaped fine dimple having a mirror surface can be formed on the surface of the glass substrate.
JP 2005-283993 A

However, in the conventional method using both laser processing and etching processing, only a concave lens shape can be formed on the surface of the glass substrate.
The present invention has been made in consideration of such circumstances, and an object thereof is to provide a geometric pattern forming method capable of forming a desired geometric pattern on the surface of a workpiece.

The geometric pattern forming method of the present invention is a first method of irradiating a workpiece with a laser and forming a plurality of depressions on the surface of the workpiece in an array having a two-dimensional periodicity at intervals. And a second step of etching the workpiece, and continuing the etching until the recesses extending around each of the recesses interfere with each other and the boundary of the recesses has a predetermined geometric pattern, It is characterized by providing.
When etching in the second step is started, generation of a concave shape centering on each depression formed in the first step starts on the surface of the workpiece. The diameter of the circumference of each concave surface increases with the progress of etching, and finally the circumferences of adjacent concave surfaces interfere with each other. When two concave surfaces interfere, the boundary between the concave surfaces passes through the midpoint of the line connecting the centers of the concave surfaces, and converges to a straight line orthogonal to this line (that is, a straight line in which both centers are line-symmetric). To do. For this reason, the entire boundary of the concave surface interferes with other concave surfaces, and the boundary of the concave surface becomes a polygonal shape. Further, the polygonal shape is determined by the arrangement of the depressions in the first step.

In the geometric pattern forming method of the present invention, it is preferable that the laser irradiated in the first step is a femtosecond laser.
Since the irradiation time of the femtosecond laser is extremely short, no thermal influence is exerted around the depression of the workpiece when the depression is formed, and damage or tissue destruction around the depression does not occur. Therefore, an accurate geometric pattern is formed by etching.

In the geometric pattern forming method of the present invention, the etching performed in the second step is preferably isotropic etching.
In the case of isotropic etching, the formed geometric pattern is easy to predict, and the formation position of the depression in the first step is easy to calculate.

In the geometric pattern forming method of the present invention, the workpiece is preferably glass.
Since the glass is etched isotropically, the formation position of the depression in the first step is easy to calculate.

In the geometric pattern forming method of the present invention, a regular triangle, square, rectangle or regular hexagon can be formed as the geometric pattern.
These polygons can be formed with high accuracy using the geometric pattern forming method of the present invention.

According to the geometric pattern forming method of the present invention, a desired geometric pattern can be accurately formed on the surface of a workpiece without requiring a large-scale apparatus or a complicated process requiring labor.
This geometric pattern forming method is particularly suitable for high-mix low-volume production.

An embodiment of a geometric pattern forming method of the present invention will be described with reference to the drawings.
FIG. 1 shows a laser apparatus used for forming a depression in a workpiece in this geometric pattern forming method.
This apparatus includes a femtosecond laser 10, a λ / 2 plate 11, a Glan laser prism 12 that prevents incident light from being reflected through the same optical path, an ND filter 13 that adjusts the amount of light, and mirrors 15 and 16. A CCD camera 19 for photographing, a lens 18 that focuses on the camera position, a dichroic mirror 17 that branches a BRG component of visible light, a condensing lens 20 that adjusts the focus of the laser, and a workpiece 30. And a control device 22 for controlling the femtosecond laser 10 and the processing stage 21.

The femtosecond laser 10 uses an apparatus with specifications of wavelength (λ) = 775 nm, repetition frequency (f) = 1 kHz, pulse width 200 fs, and average output 800 mW.
The processing stage 21 uses an air static pressure triaxial linear stage and has a performance of 10 nm resolution.
The control device 22 controls the movement of the processing stage 21 and the timing of laser oscillation in synchronization so that laser irradiation can be performed on a desired portion of the workpiece 30.
The workpiece 30 is made of quartz glass (thickness: 1.5 mm) with less impurities so that unevenness does not occur during etching.
In order to form an equilateral triangle, a square, a rectangle, or a regular hexagonal fine geometric pattern on each of the workpieces 30, a laser is applied to the workpiece 30 while controlling the irradiation position using the apparatus of FIG. 1. Were irradiated to form a number of depressions distributed two-dimensionally on the surface.

  In FIG. 2, the laser irradiation position (dent formation position) corresponding to each geometric pattern is indicated by black dots. Since the equilateral triangle forms an equilateral triangle having a side of 20 μm, the distance from the adjacent laser irradiation position was set to L1 = 11.55 μm and L2 = 20 μm. In order to form a regular square having a side of 10 μm, the regular square was set such that the distance from the adjacent laser irradiation position was L1 = 10 μm and L2 = 10 μm. In order to form a rectangle of 10 μm × 15 μm, the distance from the adjacent laser irradiation position was set to L1 = 10 μm and L2 = 15 μm. Further, since the regular hexagon forms a regular hexagon having a side of 5.8 μm, the lengths of L1 and L2 shown in FIG. 2 are set to L1 = 8.66 μm and L2 = 5 μm.

Since it is necessary to form many identical fine geometric patterns on the actual workpiece 30, the unit structure at the laser irradiation position shown in FIG. Each position obtained by repeating in the direction is irradiated with a laser. Therefore, by this laser irradiation, a large number of depressions are two-dimensionally and periodically arranged on the surface of the workpiece 30.
Here, as shown in the processing conditions of FIG. 3, a condenser lens 20 of f = 8 mm (NA = 0.5) is used, laser output: 10 mW, processing range of the work piece 30: 200 μm × Each workpiece 30 is irradiated with a laser by setting it to 200 μm. Regardless of which recess corresponding to any geometric pattern was formed, laser processing on each workpiece 30 was completed in a few minutes.

The workpiece 30 having the depressions is then etched.
First, changes due to etching of the dimple shape formed on the workpiece 30 will be described.
FIG. 4 shows the results of a simulation in which changes in the dimple shape are traced over time. 4A shows how three dimples arranged at equal intervals are etched at an etching rate of 1 μm / h, and FIG. 4B shows the relationship between the time and the diameter and depth of the dimple. Is shown.
The initial dimple has a depth of 4 μm and a diameter of 4 μm, and the dimple shape is approximated by y = x ² .

In FIG. 4A, the surface before etching is indicated by a line 40, and the surface for every hour of etching is indicated by a line 41. In FIG. 4B, the temporal change in the dimple depth is indicated by a black triangle, and the temporal change in the dimple diameter is indicated by a white circle.
The diameter of the dimple is initially widened by etching, but after 4 hours, the flat portion in the middle between the dimple and the adjacent dimple disappears completely, and thereafter, the diameter of the dimple does not change. Eventually, the diameter of the dimple converges to the center distance between the dimple and the adjacent dimple.
On the other hand, the depth of the dimple does not change while the diameter of the dimple continues to increase, but when it is 5 hours or longer, the convex portion at the intermediate position between the dimple and the adjacent dimple decreases according to the etching time, The dimple depth becomes shallower. Also, the dimple curvature decreases with the etching time.

As shown in the processing conditions of FIG. 3, the actual etching uses a mixed solution of hydrofluoric acid and sulfuric acid (1: 1, 3 wt% each) as an etching solution for the quartz glass of the workpiece, and a hot stirrer. Was carried out with stirring and heating. The heating temperature is about 40 ° C., and the rotational speed of stirring is 350 rpm.
FIG. 5 shows SEM images at various points in time when a regular hexagonal dimple array was produced. In addition, the workpiece in the figure was observed with an inclination of 30 °, and substantially the same position was observed for each etching time.
The dimples before etching are elliptical, but it can be seen that the dimples become spherical as the etching progresses. In the etching for 3 hours, the roughness component generated by laser irradiation spreads, and the inside of the dimple becomes temporarily rough. In the 5-hour etching, the enlarged dimples come into contact with each other and approach the regular hexagon as designed. If etching is further continued, the dimple becomes a mirror surface.

Similarly, FIG. 6A shows the SEM image of the depression before etching and the state after 15 hours of etching when an equilateral triangle dimple array was produced, and FIG. 6B produced a square dimple array. FIG. 6C shows a similar SEM image when a rectangular dimple array is manufactured, and FIG. 6C shows a similar SEM image when the rectangular dimple array is manufactured.
In either case, a mirror dimple array having a desired shape can be manufactured by performing etching.
FIG. 7 shows an error between the actually measured value of each geometric pattern produced and its design value. The length of the side of the produced dimple is within 2% of the design value. The dimple depth is about 1 μm in all cases. It is inferred that the variation in shape depends on the variation in the depth of adjacent dimples.

Thus, in this geometric pattern forming method, a fine geometric pattern having a selected shape can be formed on the surface of the workpiece.
The workpiece is preferably glass that is isotropically etched. In particular, quartz glass is preferable. When the etching proceeds isotropically, the formed geometric pattern can be easily predicted, and the formation position of the depression by laser irradiation can be easily calculated. However, a material other than glass may be used as a workpiece.
Moreover, it is preferable that the laser for forming the depression on the surface of the workpiece is a femtosecond laser. Since the irradiation time is very short, the femtosecond laser does not exert a thermal influence around the depression of the workpiece when the depression is formed. Therefore, damage does not occur around the depression, and an accurate geometric pattern can be formed by etching. Further, even if the workpiece is quartz glass, stable laser processing is possible. However, in the present invention, it is possible to use a laser other than the femtosecond laser.

The geometric pattern forming method of the present invention can be used to improve the function by forming a fine pattern of a desired shape on the surface of an object, or to manufacture a surface functional product that realizes a new function. In addition, as one of the surface functional products, it can be used for the manufacture of optical devices that exhibit low reflectance and high transmittance and optical properties that exhibit high reflectance and low transmittance.
The method of the present invention can be used for manufacturing a concave spherical lens array by appropriately setting the size of the geometric pattern.
In addition, it can be expected to be applied as a tray for precise arrangement of fine particles, cells, etc., such as DNA microarray and biochip.

  INDUSTRIAL APPLICABILITY The present invention can accurately form a desired geometric pattern on the surface of an object, and can be widely used for manufacturing various surface functional products, optical instruments, precision array trays, and the like.

Schematic diagram of a laser apparatus used in the geometric pattern forming method of the embodiment of the present invention The figure which shows the relationship between the target shape and laser irradiation position which are formed with the geometric pattern formation method of embodiment of this invention The figure which shows the processing conditions in the geometric pattern formation method of embodiment of this invention The figure which shows the relationship (b) of the etching shape change (a) obtained by simulation of the geometric pattern formation method of this invention, and etching time and a process shape. The figure which shows the SEM image of the preparation process when a regular hexagonal dimple array is produced with the geometric pattern formation method of embodiment of this invention. The figure which shows the SEM image of the equilateral triangle dimple array (a), the square dimple array (b), and the rectangular dimple array (c) which were produced with the geometric pattern formation method of embodiment of this invention. The figure which shows the shape evaluation of the geometric pattern produced with the geometric pattern formation method of embodiment of this invention The figure explaining the shape change of the dimple array by etching The figure which shows the SEM image of the hollow (a) formed by laser irradiation to soda-lime glass, and the concave shape (b) obtained by etching

Explanation of symbols

10 femtosecond laser 11 λ / 2 plate 12 Glan laser prism 13 ND filter 15 mirror 16 mirror 17 dichroic mirror 18 lens 19 CCD camera 20 condenser lens 21 processing stage 22 control device 30 workpiece 40 surface before etching 41 etching Surface every hour 100 Glass substrate surface before etching 110 Recess before etching 120 Substrate surface in which etching has progressed 130 Recess in etching (dimple)

Claims (5)

A first step of irradiating the workpiece with a laser and forming a plurality of depressions on the surface of the workpiece in an array having a two-dimensional periodicity at intervals;
A second step of etching the workpiece, and continuing the etching until the recesses extending around each of the recesses interfere with each other and the boundary of the recesses has a predetermined geometric pattern;
A geometric pattern forming method comprising:   2. The geometric pattern forming method according to claim 1, wherein the laser irradiated in the first step is a femtosecond laser.   3. The geometric pattern forming method according to claim 1, wherein the etching performed in the second step is isotropic etching. 4.   4. The geometric pattern forming method according to claim 1, wherein the workpiece is glass.   5. The geometric pattern forming method according to claim 1, wherein the geometric pattern is a regular triangle, a square, a rectangle, or a regular hexagon.